1. Field of the Invention
The present invention relates to epoxy resin compositions containing a polyphosphoric/polyphosphonic anhydride curing agent. As used herein, the term "polyphosphoric/polyphosphonic anhydride" is intended to encompass those polymeric anhydrides formed by reaction of phosphorus pentoxide with neutral phosphate esters and neutral phosphonate esters.
2. Description of the Prior Art
U.S. Pat. Nos. 3,454,683 and 3,454,684 and British Patent No. 1,064,610 describe the preparation of neutral polyphosphoric anhydride compositions by reacting phosphorus pentoxide with one or more phosphorus compounds (e.g., trialkyl phosphates or phosphonates). The polyphosphoric anhydrides are described as useful as catalysts in proton-catalyzed reactions or as intermediate products in the manufacture of insecticides.
There are certain disclosures in the prior art of using phosphorus-containing compounds in epoxy resin compositions.
Japanese Patent Publication No. 58 173,149 teaches epoxy resin compositions using phosphate, phosphite or polyphosphate additives as moisture or corrosion inhibitors. This reference indicates that the compositions consist essentially of epoxy resin, hardener, inorganic filler, and corrosion or moisture resistance additive. The additional mention of a hardener, in addition to the phosphate, phosphite or polyphosphate additive, indicates that such phosphorus-containing additives were not deemed to be curing agents for the epoxy composition. The phosphorus-containing additives actually tested did not include neutral polyphosphoric anhydride compositions.
U.S.S.R. Patent No. 455,129 indicates that the mechanical and physical properties of epoxy resin compositions and its resistance to fire can be improved when mono-, di-, or tri-alkylophosphines are used as hardeners in amounts of from about 10-25% by weight.
U.S.S.R. Patent No. 1,000,891 teaches the use of a phosphorus-containing polyester as an epoxy resin hardener. A representative example of such a phosphorus-containing material is polypentamethylene phosphite which is obtained by the polyesterification of dimethyl phosphoric acid with hexane diol.
Japanese Patent Publication No. 62 250 026 shows certain low room temperature curable epoxy resin compositions which contain a silyl phosphate ester or silyl polyphosphate ester material as a hardener and crosslinking agent.